Implement rename, renameat, renameat2

Added new rcp "insert_node" to insert new metadentry into the metadata DB.
This call differs from the "mk_node" because it will insert the metadata
received from the caller instead of generating them assuming that they
have been generated previously.

It can be used to move entries between metadata nodes

add checks for directory existance before to remove it

remove_node RPC can now be used to remove only the metadentry from the
metadata DB without touching the relative data in the ChunkStorage.

 - ChunkStorage now use file ID to organize chunks and locate them
 - all the data rpc now accepts the file ID instead of the file path

The OpenFile and Metadata class have now a fuid field that is a unique file identifier. The fuid is generated by a metadata daemon when the new node is created.

Syscall logging allows to log all syscalls but this will slow down the
execution.

Syscalls logging needs now to be explicitely enabled through the
definition of LOG_SYSCALLS at compile time.

readlink write at most PATH_MAX, thus we need to support also the worst case
scenario in which all the bytes are written.

ensure rpc_addresses object have been initialized before we use it for
the first time

Instead of passing only the mode as paramenter, we now pass an entire
Metadata object in such a way that the parameter can be configured at
compile time. For instace if we support symlinks we would like also to
pass the target path

the functionality wasn't used at all and it will be implemented later
with a different approach

this patch was resolving the 100% CPU bug [1]

But it was also introducing invalid read inside mercury library. Thus
from time to time it could led to segmentation faults.

[1]: https://github.com/mercury-hpc/mercury/issues/229

Can be used to retrieve the Metadata object for a named path

In several places the adafs_stat function have been replaced with this
new adafs_metadata. This allowed to avoid the construnction of the
additional `struct stat`.

This allowed to avoid improper static_cast to check downcasting

Metadata class needs to be used by both the client and the daemon

The metadata class needs to represent metadata of a file,
thus it shouldn't contain the path itself. In fact we actually didn't
use it at all.

This will make further refactoring easier and it save some memory copies.